Now Ryan Turner, a Volt owner and regular reader of this site, suggests that the Volt has an unaddressed issue that could potentially pose a safety hazard under certain circumstances.

The same issue, in fact, applies to every hybrid and plug-in hybrid car whose engine may stay off some of the time.

It has to do, Turner says, with the Volt's keyless entry system. It appears that a number of Volt owners have forgotten to turn their car off at one point or another.

When the Volt is operating on battery power, the engine doesn't run, so aside from dashboard lights, there's very little to remind owners that the car is on.

In a highly unscientific poll of Volt owners, Turner found that roughly one in three admitted to having stepped away from their car without turning it off.

In a pure electric car, this wouldn't be an issue; the car would eventually shut itself down to protect the battery. But the Volt, Turner says, will stay on until the battery depletes, at which point its engine will switch on.

In one thread on a Volt forum, an owner recounts forgetting to turn the car off, and returning to find the engine running and the garage filled with carbon monoxide and exhaust fumes only a few hours later.

Kevin Kelly, GM's Manager, Electric Vehicle and Hybrid Communications, explained that it's a standard feature of any car with a pushbutton start and a proximity-sensing system with a keyless fob to say on even if the fob is removed from the car.

He posed the scenario of a broken-down car with a family inside.

If the driver leaves to get help, taking the fob, it's important that the car can stay running so the heater or air conditioner works and the remaining occupants don't freeze or broil.

Kelly noted that if the Volt is on and the driver's door opens--indicating that the driver may be about to depart--the chime that sounds is louder than any other warning the car makes.

And there's a secondary alert system as well, he said: If the fob remains inside the car, but the driver's seat sensor indicates that the seat isn't occupied and the driver's door closes, the horn chirps twice, again louder than the normal volume of the pedestrian-alert chirp.

Turner counters that these "audible cues are minimal, and if you are distracted or there is noise around you, the car will seem to be off."

"Many people, like myself, end up getting out of their car to get the mail, then driving the car into the garage," he says.

While he acknowledges the warnings, Turner says, "We get used to all the internal beeps of the car, and become use to it to the point of ignoring it."

Turner wants the Volt to warn owners more aggressively, with "very distinct honking" to alert the driver.

While he would like a system to power down the car, he acknowledges that " it would have to be carefully done; you don’t want to have a child killed from heat exposure when you quickly go into a store to pick up a soda and the car decides to cut itself off."

Finally, Kelly pointed out, the same "on but silent" scenario is hardly confined to the Chevy Volt; it applies to every hybrid or plug-in hybrid that has a proximity fob and push-button start.